I don't think *anyone* has said that passing the exam makes them a good / safe / nor knowledgeable boater.
Where is this coming from? I have never seen anyone that has said this.
All it proves is that you read the materials, and passed the exam. It doesn't mean you can remember the information, nor does it prove that you follow the practices presented in the course.
After passing the exam and after boating for a few years, I still am trying to learn everything that I can. I'm the last person to say that I know what I'm doing.
Most people that I know will also say the same thing, that it is a continual learning process that never ends.